1. Field of the Invention
The present invention relates to paper machine clothing and a process for joining a paper machine clothing, and more particularly, to joining processes used to join ends of a paper machine clothing in an endless manner.
2. Description of the Related Art
A paper machine clothing (PMC) base fabric, such as for a press fabric or a forming fabric, is typically manufactured with a specific set of design and quality specifications for a particular paper machine's performance requirements. These specifications include specific dimensions, surface characteristics, open area, void volume, permeability and smoothness, among others.
The purpose of a press fabric in a paper making machine is to transport water away from the fibrous material web. The press fabric travels with the fibrous web through a press section of the paper machine where pressure is applied to the fibrous material web and press fabric traveling therewith in order to remove as much liquid or water as possible from the web. Accordingly, it is important to provide a fabric having a substantially uniform surface structure in order to avoid marking of the fibrous web from pressing.
It is known in the art to manufacture a woven press fabric having a flat woven base fabric with a plurality of warp yarns forming seam loops along the ends of the fabric extending in a cross machine direction, transverse to the machine direction. The ends are then placed in end-to-end disposition in order to interdigitate the loops and a pintle wire is then inserted in the interdigitated loops to lock the ends together to bring the fabric into an endless form. For installation in a paper machine of the like, the two ends are separated such that the fabric can be pulled in its direction of movement into the machine, after which the two belt longitudinal ends can then be joined together again. The region of the seam in this case has a larger void area than the rest of the fabric, resulting in a differential dewatering in this area which may lead to marking of the fibrous web. In addition, the formation of seam loops on the base fabric results in increased production time and expense.
Further, it is known from international publication EP 1 579 066 to manufacture a press felt from a base fabric including a plurality of machine direction (MD, warp) yarns and cross machine direction (CD, weft) yarns. To form the press fabric, the two ends of the planar fabric are then overlapped and heat is applied to melt bond the threads. During the application of heat, the joining ends areas of the base fabric may be pressed so that the thickness of the overlapping joining ends areas substantially corresponds to the thickness of the rest of the fabric. It is further known from EP 1 579 066 to manufacture the base fabric with a thinned portion, where the density of transverse yarns is smaller on the ends than the rest of the base fabric, so that the thickness of the overlapping joint is decreased.
What is needed in the art is an improved joining process for a paper machine clothing base fabric which improves the life expectancy of the fabric while reducing the risk of sheet marking by providing a substantially uniform air permeability, caliper, mass and density.